Method of making plural potentiometer body

ABSTRACT

A plural potentiometer in which independently and infinitely variable potentiometers are included in a common housing where for each potentiometer a resistive strip is applied to the inside of the housing and a leadscrew wiper nut, wiper, terminals and bearings are associated with each resistive strip to define the separate potentiometers. The leadscrews are suspended by bearings in end plates of the housing and independent means to turn each leadscrew is included.

United States Patent Beetle 1 1 Se t. 16 1975 [54] METHOD OF MAKING PLURAL 2,962,393 1 1/1960 Ruckelshaus 338/308 X POTENTIOMETER BODY 3,172,074 3/1965 Drewes et al. i 338/308 3,481,306 12/1969 OConnell et a1... 29/620 X Inventor: Arthur Beetle, St. Petersburg, 3,648,216 3/1972 Rector 29/620 x Fla.

[73] Assignee: TRW Inc., Cleveland, Ohio primary Examiner victor ip [22] Filed: July 11, 1974 Attorney, Agent, or FirmLawrence S. Cohen, Esq.

Appl. No.: 487,610

Related US. Application Data Division of Ser. No. 408,097, Oct. 19, 1973, Pat. No.

US. Cl. 29/620; 338/308; 338/311 Int. Cl. HOlC 17/06 Field of Search 29/620, 621, 610; 338/311,

References Cited UNITED STATES PATENTS 6/1930 Stoekle 29/620 X [57] ABSTRACT A plural potentiometer in which independently and infinitely variable potentiometers are included in a common housing where for each potentiometer a resistive strip is applied to the inside of the housing and a leadscrew wiper nut, wiper, terminals and bearings are associated with each resistive strip to define the separate potentiometers The leadscrews are suspended by bearings in end plates of the housing and independent means to turn each leadscrew is included.

6 Claims, 9 Drawing Figures PMEM'; SE? 1 R W SEiZU 1 OF 2 FIG.

FIG. 2

FIG. 5

FIG. 4

PATENTEDSEP 161875 sum 2 [1f 2 FIG. 7

FIG. 6

FIG. 8

METHOD OF MAKING PLURAL POTENTIOMETER BODY This is a division of application Ser. No. 408,097 filed Oct. 19, 1973, now US. Pat. No. 3,846,733.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to plural potentiometers and more particularly to a plural potentiometer where each potentiometer is independent and is infinitely variable.

2. Description of the Prior Art Plural potentiometers of the prior art consist generally of a single varying means and one or more resistive elements associated therewith. Such potentiometers usually require that all the resistors be varied if any one is to vary. While different resistance values can be given to the various resistive elements, so that each can give a different value at any one setting; nevertheless they are interdependent.

In another aspect of the prior art, potentiometers have been ganged by gears to a single adjuster. By putting a clutch or some other disengaging means between the shaft and the gears individual potentiometers may be subtracted from the gang. Such systems while useful for some purposes have the disadvantage of requiring relatively complex mechanism and concomitantly complex operability in a package large by standards of modern electronic packaging.

SUMMARY OF THE INVENTION The present invention provides a plurality of potentiometers each of which may be varied ,by its own independent adjustment. They are all packaged and may be sealed in a single housing. External terminals permit convenient wiring to a circuit. Resistive strips are applied to the inside of the housing with a leadscrew, wiper nut, wiper terminals and bearings associated with each resistive strip so that by turning the leadscrew the wiper traverses the resistive strip effecting a variation in resistance in the circuit in which the potentiometer may be included. The leadscrew and its bearings are mounted in end plates of the housing with means to rotate the leadscrew at one end thereof.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view of half of the housing of a preferred embodiment.

FIG. 2 is an end view of the assembled housing of a preferred embodiment.

' FIG. 3 is an end view of the adjustment end of a preferred embodiment.

FIG. 4 is a partial sectional view through 44 of FIG. 3.

FIG. 5 is a view of an embodiment of the terminal means taken as a partial sectional view through 5-5 of FIG. 4.

FIG. 6 is apartial sectional view of the housing at one stage of the process.

FIG. 7 is a partial sectional view of the housing at another stage of the process.

FIG. 8 is a view of the shaft assembly.

FIG. 9 is a view of the wiper nut.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in FIGS. 1 and 2, a cylindrical housing 1 is made up of separate split halves 1a and lb. The split halves may be made with a positive mating joint such as the rabbit joint 2. This joint assures accurate, fast assembly. For most purposes a high temperature sealing material such as an epoxy should be used to join the split halves. The housing is preferably made of a nonconductive material or the materials generally known as dielectric materials. A ceramic material is preferred.

A plurality of resistance strips 3 are formed on the inside surface 4 of the housing 1. A method of forming the resistance strips will be discussed below. For this explanation, eight potentiometers are described. Thus, eight resistance strips are formed on the surface 4, four on each half of 1a and 1b of the housing 1. The strips run axially along the inside surface, being generally parallel to each other and to the longitudinal axis of the cylindrical housing.

Referring to FIGS. 3 and 4, the housing is closed and sealed at its ends by a first end plate 5 and a second end plate 6. In this case again rabbit type joints 7 and 8 are suggested for ease of assembly and, with a good sealing material, dependable sea].

In this preferred embodiment, the first end plate 5 may be of an electrically conductive material such as steel while the second end plate should be a nonconductive, such as ceramic or other dielectric. Mounting holes such as at 9 may be conveniently provided although it is contemplated that for particular applications one or both of the end plates may be variously shaped for mounting purposes.

The eight lead screws 10 are located inside the housing between the end plates 5 and 6 and each one spaced from its associated resistance strip radially inward with respect to the axis of the housing. Thus, as shown in FIG. 3 the lead screws 10 are arranged in a circle concentric with the housing.

Each of the eight leadscrews 10 are fitted identically so that the following description applies to all of them. Referring to FIGS. 4 and 8 the leadscrew 10 is secured at one end in the first plate 5 by a shaft end 11 rotably mounted in a hole 12 in the plate 5. The shaft end 11 is made of an insulating material such as nylon. The shaft end 11 is secured against axial motion by a shaft retaining pin 13 seated in hole 14 of the plate 5 and extending into a groove 15 in the shaft end 11. The shaft end 11 and the leadscrew 10 are connected by a reduced diameter portion 16 of the leadscrew 10 tightly fitted in a hole 17 in the shaft end 11.

The exposed end 18 of the shaft end 1 1 has some provision for its being rotated. In this case a screwdriver slot 19 is shown. The shaft end 11 may protrude from the end plate 5 as shown in the figures, or it may be flush or recessed, so long as some means is provided for rotating.

The shaft retaining pin 13 is secured against backing out of the hole 14 by placing a drop of epoxy or paint in the hole after the pin is in place.

It is apparent from this description that the leadscrew 10 is electrically isolated from the end plate 5 by the insulated shaft end 11, but that other means could be used to accomplish this.

The leadscrew 10 is mounted at the second end plate 6 in a combination wiper terminal and shaft bearing 20. This terminal is mounted in the end plate 6; its external portions being of a commonly known variety and like the terminals 28 to be described below.

Inside the end plate 6 the wiper terminal 20 has a lip 21 which holds a shaft end wiping contact 22 against the end plate 6. The wiping contact also bears on the shaft end contact 29 of the leadscrew 10. The shaft end contact 29 is preferably of semi-precious metal. The leadscrew l terminates in a reduced diameter portion 23 which extends into the hole 24 of the combination wiper terminal and shaft bearing 20.

On the threaded portion 25 of the leadscrew there is a wiper nut 26 also shown in FIG. 9, having a wiper 27 preferably of semi-precious metal which bears on the resistance strip 3.

As shown in FIG. 5, a terminal 28 is fitted through the housing to contact one end of the resistance strip 3. A second terminal may be fitted at the other end of the resistance strip. The exposed or external portions of the terminals 28 may be chosen from the commonly known varieties. They extend through the housing, although preferably not through the resistance strip 3 but rather beside it. A tab 30 is secured such as by welding or brazing to the end of the terminals 28 to the resistance strip 3. Other means for terminating may be chosen.

In use the eight potentiometers of the preferred em bodiment herein described are wired into electrical circuits as desired and known to those familiar with them by means of the terminals, and the electrical resistance value of each potentiometer is varied as desired by rotating the insulated shaft end and with it the leadscrew. The wiper nut and wiper do not rotate being held against rotation by bearing force against the housing 1 and the resistance strip 3 of the wiper. Other means, such as a mechanical stop may be employed to prevent rotation of the wiper. As the leadscrew 10 is rotated the wiper nut 26 and wiper 27 translate axially, thereby varying the amount of the resistance strip included in the circuit and consequently the resistance in the circuit.

The multiple potentiometers are adapted to a process manufacture which is also part of the invention as hereafter described in its preferred embodiments.

The ceramic tube or cylinder halves la and lb are coated on their inside surface with a vitreous enamel resistance material or glaze such as is well known to those familiar with the art. In particular, the tube may be coated with a dip glaze by coating the entire part and then wiping off all but the inside surface 4. Then the parts are processed through a firing operation to cure the glaze. Thereafter the glaze material is removed from the areas 31 as shown on FIGS. 1 and 2 leaving only the resistance strips 3. This removal step may be done by vapor honing, sandblasting or other means, as desired. Finally, the electrical resistance of each of the strips is adjusted in a known manner to the desired range or resistance by removing some of the resistance material. It is similarly possible to adjust the resistance values of each of the resistance strips so that different total resistance values may be obtained in one package.

In another embodiment of the process as shown in FIGS. 6 and 7 the housing is formed with grooves thereby providing a spline-like structure as shown, including a root 32 and a crest 33. The entire inside surface is coated with a resistor glaze material 34 and fired as described above. Then the resistor glaze material is removed in a single step or pass from the crests 33 such as by diamond honing or other reaming process leaving only the resistor glaze material 35 left in the grooves, forming the resistance strips. These are adjusted to the desired resistance as previously described.

By this invention a number of independently and infinitely variable potentiometers may be included in a single package of such small size to be useful with the complex and compact electronic packages in current use. The number of potentiometers in a unit of the invention and indeed the preferred embodiment de scribed herein may be modified without departing from the essential nature of this invention and all changes and modifications which do not constitute departures from the scope of the invention are intended to be covered by the appended claims.

I claim:

1. The process of making a plural leadscrew potentiometer body including forming independent axial vitreous enamel resistance strips on a body having an elongated intemal surface comprising;

applying a vitreous enamel resistance mixture to the internal surface; curing the mixture to form a vitreous enamel resistance glaze material, selectively removing areas of the resistance material in axial strips parallel to the elongated dimension of the external surface thereby leaving bare strips between the remaining independent strips of the resistance material. 2. The process of claim 1 wherein the resistance material is removed by vapor honing.

3. The process of claim 1 wherein the resistance material is removed by sandblasting.

4. The process of making a plural potentiometer body including forming independent axial strips of resistance material on a body having an elongated internal cylindrical surface comprising;

forming on the elongated internal cylindrical surface a plurality of axially extending grooves and crests therebetween;

applying the material to be formed into strips to the internal surface;

removing the material from the crests thereby leaving independent strips of the material in the grooves.

5. The process of claim 4 whereby the material is a vitreous enamel resistance mixture and is cured before the removal step and the removal step comprises passing a removing tool axially through the body and removing the cured material from the crests and thereaf ter adjusting the resistance of the strips remaining in the grooves.

6. The process of claim 5 wherein the cured material is removed from the crests by passing a diamond hone axially through the body. 

1. The process of making a plural leadscrew potentiometer body including forming independent axial vitreous enamel resistance strips on a body having an elongated internal surface comprising; applying a vitreous enamel resistance mixture to the internal surface; curing the mixture to form a vitreous enamel resistance glaze material, selectively removing areas of the resistance Material in axial strips parallel to the elongated dimension of the external surface thereby leaving bare strips between the remaining independent strips of the resistance material.
 2. The process of claim 1 wherein the resistance material is removed by vapor honing.
 3. The process of claim 1 wherein the resistance material is removed by sandblasting.
 4. The process of making a plural potentiometer body including forming independent axial strips of resistance material on a body having an elongated internal cylindrical surface comprising; forming on the elongated internal cylindrical surface a plurality of axially extending grooves and crests therebetween; applying the material to be formed into strips to the internal surface; removing the material from the crests thereby leaving independent strips of the material in the grooves.
 5. The process of claim 4 whereby the material is a vitreous enamel resistance mixture and is cured before the removal step and the removal step comprises passing a removing tool axially through the body and removing the cured material from the crests and thereafter adjusting the resistance of the strips remaining in the grooves.
 6. The process of claim 5 wherein the cured material is removed from the crests by passing a diamond hone axially through the body. 